Design

Subjects

All women who had a low birthweight infant (<2500 g) (index birth) and a subsequent liveborn infant (outcome birth) in Denmark between 1980 and 1992 (exposed cohort, n=11 069) and a random sample of the population who gave birth to an infant weighing =2500 g and to a subsequent liveborn infant (unexposed cohort, n=10 211).

Main outcome measures

Risk of having a low birthweight infant in the outcome birth as a function of changes in male partner, area of residence, type of job, and social status between the two births.

Results

Women in the exposed cohort showed a high risk (18.5%) of having a subsequent low birthweight infant while women in the unexposed cohort had a risk of 2.8%. After adjustment for initial social status, a decline in social status increased the absolute risk of having a low birthweight infant by about 5% in both cohorts, though this was significant only in the unexposed cohort.

Change of male partner did not modify the risk of low birth weight in either cohort Conclusion : Having had a low birthweight infant and a decline in social status are strong risk factors for having a low birthweight infant subsequently.